High-Resolution Analysis of Earthquake Source Processes Using 3-D Green's Functions

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In order to know detailed source processes with high resolution, we have to analyze high-frequency ground motions reflecting them. This implies that we have to carry out analyses using Green's functions calculated in a realistic 3-D underground structure, because the details of the structure are effective on high-frequency ground motions. In this study we have developed a method of high-resolution analysis of source processes with 3-D Green's functions, and applied it to observed records of large earthquakes in Japan. In 2003, we made a 3-D structure model and developed the voxel finite element method. We then applied them to the 1995 Kobe earthquake for their verification. In 2004, we further applied them to records of recent earhquakes in and outside Japan (Miyagi ken Hokubu earthquake, Tokachi-oki earthquake, Duzce earthquake, etc.). We first performed preliminary analyses using Green's functions for a 1-D structure model and a halfspace, and then applied 3-D Green's functions. However, it is difficult to construct the 3-D models and it takes a long time to numerically compute Green's functions in them. So we made various 1-D models for observation stations and combine them into a pseudo-3D model. (Hikima and Koketsu, 2005). We carried out high-resolution analyses of the mainshocks and aftershocks of the Miyagi-ken Hokubu and Chuetsu earthquake sequences using these pseudo 3D Green's functions. The west off Fukuoka prefecture earthquake occurred on March 20, 2005 near the end of the project term. We verified the method developed by applying it to this earthquake.